Patent GB-736464-A (GB)
Title: Improvements in or relating to ultrasonic test arrangements
IPC: G01N29/06
Filed: 1953-07-23
Abstract: 736,464. Ultrasonic inspection devices ; con trolling and actuating apparatus by ultrasonic waves. SIEMENS - REINIGER - WERKE AKT.-GES. July 23, 1953 [July 25, 1952; July 16, 1953], No. 20528/53. Class 118 (2). In a system for detecting flaws in strip material in which ultrasonic pulses are transmitted through the strip, the presence of a defect being indicated by a diminution of the intensity of the received pulses, a linear array of transmitting transducers coupled to an electronic pulse generator is disposed on one side of the strip transversely thereto and a corresponding array of receiving transducers is disposed on the other side of the strip, the system being such that the pulses received at the separate receiving transducers due to a single pulse from the pulse generator are displaced in time. The receiving transducers are coupled to a common amplifier whose output may be coupled (a) to the Y plates of a cathoderay oscilloscope whose time-base is synchronized with the pulse generator and/or (b) via separate gated amplifiers to separate visual or aural alarms. The transducers are preferably immersed in water in a tank having slots in opposite sides through which the strip is fed continuously, leakage through the slots being reduced by rubber flaps, Fig. 10a (not shown), and means are described for automatically stopping the strip feed or for marking the strip when a flaw is encountered. In one embodiment, Fig. 2, the distances of the transmitting transducers QS1 ... QSn from the strip P are staggered and the receiving transducers QEI ... QEn are coupled via an amplifier V to a cathode-ray oscilloscope A to produce corresponding displaced responses JE1 ... JEn on the screen Sch, the response JE3 having an amplitude less than that of the other responses indicating the presence of a flaw F ; alternatively the transmitting transducers may be equidistant from the strip, the distances of the receiving transducers being staggered. In other embodiments, Figs. 3, 4 and 6 (not shown) and Fig. 8, the transmitting and receiving transducers are equi-distant from the strip and blocks of material having different wave transmission times (different material, same dimensions or same material, different dimensions) are attached to the faces of the transmitting or receiving transducers, Fig. 3 (not shown), or the transmitting transducers are tapped into an electrical delay line VNI, VN2, Fig. 8 and Figs. 4 and 6 (not shown), coupled to the pulse generator JG. In any of the embodiments the delays may be such that the displayed pulses partially overlap, Fig. 5 (not shown). In order to increase the lateral spacing of the transducers without causing corresponding gaps between the ultrasonic beams, the beams may be expanded and contracted by suitable lenses LS1, LS2, LE1, LE2, Fig. 8 and Fig. 6 (not shown), and in order to prevent spurious signals due to the reception at one transducer of transverse waves scattered from the other beams, an apertured absorbent plastic baffle plate G, Fig. 8 and Fig. 7 (not shown), may be interposed between the test strip and the receiving transducers. In Fig. 8 the common receiving amplifier VO is coupled to the Y plates of the oscilloscope A via amplifiers VI, V2 and VJ which are gated on during sequential periods Tl, T2 and TJ by positive pulses applied thereto from the synchronizing device S via delay devices N1, N2 and N3 which are so adjusted that the amplifiers VI, V2 and V3 pass the pulses received directly by the receiving transducers QE1, QE2 and QE3 respectively. Amplifiers V1, V2 and V3 are also coupled to relays R1, R2 and R3 controlling aural and visual alarms A1, A2 and A3 which operate only when the amplitude of the corresponding received pulse falls below a predetermined value. Alternatively, the relays may be controlled by corresponding photo-cells located in front of the screen of the oscilloscope, Fig. 9 (not shown), and the relays may also control means for stopping the strip feed mechanism when a flaw is detected or they may beconnected via further delay devices to control a corresponding array of paint nozzles spaced across the strip emerging from the tank which mark any defective portions of the strip, Figs. 10a and 10b (not shown).